[LINK] web: The NBN satellite Malcolm Turnbull never wanted prepares for liftoff

[Glen Turner]

Tom Worthington wrote:

> Perhaps someone can answer a question about the current NBN "Interim
> Satellite Service" (ISS): Why is compression OFF by default?

It's a reasonable design choice. Probably the one I'd make as it's a can
of worms for little benefit.

There's not much uncompressed data by volume on the Internet. Sizeable
data has already been compressed, often by an algorithm which performs
better than a general-purpose compression algorithm -- JPEG, GIF, PNG,
MP3, H.264 video, software packages.

In-flight compression of the remaining data is getting less and less
effective. Consider the movement to serve all HTML over TLS. This data
can't be compressed in-flight, as an encrypted stream should appear
random.

There's the issue of packet loss, an amount of which has to be expected
on a satellite link. If each packet stands alone then the effectiveness
of compression will be small (it can't "learn" the patterns in the data
from previous packets). If compression continues over multiple packets
then the loss of a packet means that a number of subsequent packets also
can't be decoded and are dropped. This in turn hints to the TCP
algorithm that the loss was due to congestion, not media loss.

-glen